A keyboard percussion instrument (KPI) such as a marimba or vibraphone comprises a plurality of keys that are held in a frame. The keys are usually arranged in two parallel rows that are oriented so that a user can reach all keys. The row nearest the user generally contains natural note keys, e.g., A, B, C, etc. while the more distant row contains flats and sharps or accidental keys, so-named because sharp and flat signs alter a note and thereby take it outside the usual course of events. A user wields at least one mallet, striking various keys to produce musical sounds. When struck, each key produces a fundamental frequency and various harmonic overtones that depend on the length of the key.
A corresponding set of tube resonators are located beneath the respective keys to enhance the sound produced when a key is struck. Each tube contains, in its top end (adjacent its respective key) a respective fan, generally a flat disk with diameter slightly less than the inner diameter of its tube resonator. The discs are mounted on a rod which is driven by a fan motor so that each disc rotates about a line contained within the plane of the disk. As each disc rotates (e.g., at 60 to 720 rpm), it alternately occludes or opens its respective tube and thereby produces a vibrato effect when its key is struck. The vibrato effect can be turned on by rotating—and off by stopping—the fan motor. Normally, the discs corresponding to the natural keys share a first rotating shaft and the discs corresponding to the accidental keys share a second rotating shaft, with both shafts rotating at the same rate.
In order for maximum sound to be produced when a key is struck while the vibrato effect is off, the fan must not block its tube. I.e., the plane of a stopped fan must be vertical or perpendicular to the axis of its tube. Heretofore various arrangements were provided to cause all discs to stop in the vertical position when the fan motor and hence the vibrato effect was turned off, but such arrangements were unreliable, awkward, and/or costly. Also I have found that vibrations from the fan motor were coupled to the fans and hence the resonators when the vibrato effect was turned on, so that the key sounds were polluted and not as pristine as possible.
The following is a discussion of some prior-art references that are believed to be pertinent. Patent references are listed in order of their issue date, indicated in parentheses.
Gladstone, in U.S. Pat. No. 1,843,553 B1 (Feb. 2, 1930), shows an early vibraphone with fan vibrato. The fans are placed in the upper ends of the resonator tubes and are called pulsators. When the operator presses a pedal, it removes a damping member from the tone bar and energizes the pulsator, causing it to rotate.
Musser, in U.S. Pat. No. 3,138,986 B1 (Jun. 30, 1964), shows a single motor that is used drive two fan shafts using one or two round belts (O Rings). This drive is quiet and rotates each shaft. However the two shafts are not kept in sync with one another. This is a problem because if one shaft is stopped with the fans in a vertical position, there is no guarantee that the other shaft will stop with the fans vertical. Having the fans vertical when the shafts are stopped is important because if the fans are horizontal, there is no sound energy transferred from the tone bars into the resonators and the sound of the instrument is muffled. Players are forced to physically rotate the fans separately to place the fans in a vertical position.
Kondoh, in U.S. Pat. No. 4,619,178 B1 (Oct. 28, 1986), shows a stop angle controller for a vibrato mechanism for a vibraphone. A circuit stops the fans at a predetermined stop angle to assure uniform non-vibrato performance.
Adams, in U.S. Pat. No. 6,596,932 B2 (Jul. 22, 2003), has a slip drive which allows the fans to be stopped when rotating without damage to the driving mechanism or the user. There is no timing belt or the ability to stop the fans on both shafts in a vertical position. Further, in order for the shafts to turn, they must be physically coupled to the driving mechanism, which means that any vibration in the driving mechanism will be transferred to the shafts. The resonators (including the fan shafts) may be removed from the rest of the instrument by pulling the slip coupling apart.
Stevens, in U.S. Pat. No. 7,732,691 B2 (Jun. 8, 2010) and U.S. Pat. No. 8,076,561 B2 (Dec. 13, 2011), shows a vibraphone where the resonator tubes with rotating fans have tube covers which can be adjusted for the amount they cover the tube openings, thereby to adjust the vibrato effect.
Shinshi, in U.S. Pat. No. 8,123,503 B2 (Feb. 28, 2012), shows the use of a permanent magnet (PM) coupling for driving a centrifugal blood pump. This is done for ease of parts replacement, simplification, low heat generation, etc.
Stevens, in U.S. Pat. No. 8,525,009 B2 (Sep. 3, 2013), shows a vibraphone with multi-function pedals having two ranges of motion. The first range controls damping and the second range controls the vibrato fans.
Zhu, in published U.S. patent application 2015/0069872 A1 (Mar. 12, 2015), shows a permanent magnet coupling with a variable gap between a cavity magnetic rotor and a disc rotor in the cavity so that the degree of coupling can be varied.
None of these references address or solve the aforenoted problems of stopping the discs in a vertical position when the vibrato function of such instruments is stopped and preventing coupling of the motor's vibrations to the resonators vertical position when the fan motor and hence the vibrato effect is turned on.